1. Field of the Invention
The present invention relates to a light-emitting device and back light unit, and more particularly, to a light-emitting device and back light unit with an incident surface having a plurality of surfaces with different normal vectors for scattering light emitted from a corresponding LED.
2. Description of the Prior Art
Commonly seen back light units are divided into direct back light units and edge back light units. Among them, the direct back light units site the light source under the LCD panel for providing a brighter light source. Therefore, the direct back light units are popularly used in large sized LCD panels such as LCD monitors and LCD TVs.
In general, the light sources of back light units are cold cathode fluorescent lamps or light emitting diodes. Cold cathode fluorescent lamps are capable of providing a large size light source. The drawbacks of a cold cathode fluorescent lamp are that it generates heat, shortens the lifetime of components, and causes mercury pollution. At the same time, the advantages of an LED are that it has a long lifetime, small size, high color saturation, consumes low power, and causes no pollution. Hence, there is a future tendency that LEDs substitute for CCFLs.
Please refer to FIG. 1. FIG. 1 is a top-view drawing of a back light unit 10 according to the prior art. The light source of the back light unit 10 is from a plurality of cold cathode fluorescent lamps 14 positioned under a light guide panel 12. The plurality of cold cathode fluorescent lamps 14 is used for generating light and the light guide panel 12 is used for evenly mixing the light delivered from the plurality of cold cathode fluorescent lamps 14. The light guide panel 12 is an injection-molded slab that is pervious to light and comprises plastic and glass materials.
Please refer to FIG. 2, which is a diagram of another back light unit 20 according to the prior art. The light source of the back light unit 20 is from a plurality of LEDs 24 (only one LED 24 is shown in FIG. 2 as an example) positioned under a light guide panel 22. The plurality of LEDs 24 is used for generating light and the light guide panel 22 is used for evenly mixing the light delivered from the plurality of LEDs 24. The light guide panel 22 is an injection-molded slab that is pervious to light and comprises plastic and glass materials. The back light unit 20 includes a diffuser sheet 26 with one side positioned at the light guide panel 22 and a reflection film 28 positioned at one side of the LED 24. The diffuser sheet 26 is used to diffuse light passing through the light guide panel and the reflection film 28 is used to reflect light generated from the LED 24. The back light unit 20 further includes a plurality of optical films 27 positioned at another side of the diffuser sheet 26. The plurality of optical films 27 at least includes an optical film selected from a group consisting of a prism sheet, a diffuser plate, a brightness enhancement film, and a ¼-wavelength sheet. The quantities and the types of the plurality of optical films 27 depend on a user's demand or design.
The cold cathode fluorescent lamps 14 are popularly used in large sized LCD panels due to the fact that they can provide a large size light source. But the cold cathode fluorescent lamps 14 generate heat, shorten the lifetime of components, and cause mercury pollution when discharging. On the other hand, although the back light unit 20 utilizing the LEDs 24 as the light source can solve the above problems, the emitting area of the LEDs 24 is too small. For this reason, the structure of the light guide panel 22 needs a special design for enlarging the emitting area of the LEDs 24.